Thermal switch



Nov. 27, 1934. H STAVE 1,982,548

THERMAL SW1 TCH Filed March 50, 1935 17.? @m j y @E /I f7 Patented Nov.27, 1934 UNITED `STATES PATENT OFFICE THERMAL SWITCH England ApplicationMarch 30, 1933, Serial No. 663,579 In Great Britain March 30, 1932 12Claims.

This invention relates to thermal switches, more especially .adapted forapplication as automatic fire detectors. The invention has for itsobjects to provide an improved device that is as before mentionedeffectively responsive both to sudden rises of temperature and to slowlongcontinued rises of temperature which exceed a definite andpredetermined limit which will be reliable in its action and will not bematerially affected by seasonal changes of temperature, so that in thecase of a fire detector, for example, the device is substantiallyequally sensitive in summer and winter.

The invention consists of an improved coni struction and ischaracterized in that two thermal elements are arranged one above or tothel side ol' the other bridging an insulating base and are soconstructed and yarranged that upon a rapid temperature change adifferential distortion of the two elements operates to establish analarm circuit through one pair of contacts and upon a slow temperaturechange a. substantially uniform distortion of both elements operates toestablish an alarm circuit through a second pair of contacts. It will beapparent that on the same principles Aa switch according to theinvention may be utiiized to open a closed circuit instead of closing'an open one by suitably arranging the thermal or heat sensitiveelement.

According to the invention, moreover, the lheatsensitive elements arepreferably of identical construction, but one may be covered or screenedunder such conditions that while it is not quickly responsive to rapidchanges of temperature, its

' capacity to vary under slow changes of temperature does not differsensibly from the capacity of the element that is not so covered orscreened.

The form of the heat-sensitive elements and the manner in which they aremounted may be varied, however, without departing from the invention.

The invention further comprises the features hereinafter described andclaimed.

The invention is illustrated, by way of example, in the accompanyingdrawing representing an automatic fire detector provided according tothe invention, and an ,installation in which such detector may be used.

Figure 1 is a sectional elevation of the yfire detector.

Figure 2 is a plan view of the fire detector.

Figure 3 is an underside plan view of the fire detector.

Figure 4 is a cross-sectional elevation on the line 4 4 of Figure l.

Figure 5 is a. moss-sectional elevation on the line 5 5 of Figure l.

Figure 6 is a diagram of one system of connections for an installationin which four of the fire detectors are provided.

In carrying the invention into effect according to one arrangement theconstruction of an automatic fire detector as illustrated in Figures 1to 5 of the accompanying drawing, there is provided a base a ofporcelain or other non-conducting material having a low co-efiicient ofexpansion and whose length and width substantially correspond with thoseof lthe thermal or heat-sensitive elements b, c. At the ends, which areadvantageously rounded, the base is provided with raised projections orbosses a1 to form seatings for the ends of the element c, the surfacesof the bosses being inclined downwardly towards the Imiddle ofthe basein order that the element c may set in position with a downwardinclination. The lower ,face of the base at the ends is formed parallelwith the inclined surfaces of the projections a1 and through the basethere are formed bores or holes Aa2 disposed in directions which arenormal to the main lower surface of the base and which in thisconstruction are of elongated cross-section in the direction of thelongitudinal axis of the base.

The elements b and c are provided as exible strips of a metal or alloyhaving a high co-eicient of expansion, such as phosphor-bronze, thestrips being in this case identical in form and mass and being mountedupon the base a by means of fixing screws or bolts a3 which pass throughthe hotes a2 in the base and engage holes in the ends of the elements b,c. Distance members d in the form of ycollars of brass or other suitablematerial are mounted upon the screws or bolts a3 between the eiements b,c for the purpose of determining the .separation of the elements. Itwill be observed that '.by reason of the inclination of the surfaces ofthe projections a1 and the correspending p'mms of the lower surface ofthe base a, the bolts or screws a3 set at an inclination to the planesof the elements b, c when the latter are firmly secured in position.

In order that the screws or bolts a3 may form part of the circuitsthrough the respective elements b, c each element is at one end formedwith a hole for the screw or bolt of a diameter sufficient to admit aninsulating washer e of mica or other suitable material. These enlargedholes are provided at opposite ends of the elements b, c that is to say,for the element c the enlarged hole for the reception ot the washer isdisposed lto the left, while in the case of the element b it is disposedto the right. In the latter instance the element is further insulatedfrom the bolt or screw a3 and its nut by mica or like washers f disposedabove and below the element, while in the case of the element c asimilar insulating washer is disposed below the collar d. The element bis provided at the middle of its length with a screwed socket g1 inwhich is received the contact screw g, the extremity of which extendsmidway between the two elements b and c and is shrouded by a sleeve ofmaterial such as steatite g2. A spring washer g3 is advantageouslydisposed between the head of the screw g and the socket gl. The elementc is similarly provided with a screwthreaded socket h1 in which isreceived a contact screw h, the upper extremity of 'which extends intothe steatite bush g2 so that it is normally positioned from theextremity of the contact screw g a distance of, for example, .00()5 ofan inch. The air gap may -readily be adjusted by rotation of the screwg. The screw h also extends downwardly with clearance in a steatite orother insulating bush i kmounted within a screw-threaded metal bush ilwhich is seated in a recess or boring a4 in the base a and is maintainedin position by a nut i2.. The bush il is screw-threaded internally forthe lower part of its bore to receive the contact screw j which may beadjusted in position by rotation. The insulating bush i may be made ofsome flexible insulating material, such, for example, asoiled silk.

VThe screws'or bolts a3 serve also to maintain on the lower face of thebase a conducting strips lc, k1, the strip lc being extendedr and formedwith a hole to receive the bush il so that it may be engaged by a nuti2.

The elements b, c are identical in form and material, 'and havetherefore precisely the same capacity for expansion, but in order thatthe device may be responsiveto rapid rises of temperature, the element cis lagged or jacketed by coverings c1 of asbestos or similarheat-insulating material. Thus the element c is protected against rapidrises of temperature and does not materially change its disposition, butthe element b, being without such protection, is caused to expandrapidly so that by its distortion or flexure the extremity 'of thecontact screw g is brought into engagement with theextremity of thecontact screw h tofclose a circuit including the screws or bolts a3 andthe strips 1c, k1. In the case of a slow rise in temperature the laggingof the ele-.- ment c is ineffective to protect the element and thus theelements b, c expand equally and together. As the result' the air gapbetween the contact screws g and h is maintained substantially constant,but the contact screw h is brought into engagement with the contactscrew j, upon a temperature rise according to a predetermined setting ofscrew j, so that a circuit is now completed by way of oneof the screwsor bolts a3, the contact screws h and y' and the strips lc, icl.

The heat-sensitive unit constructed in -the 5 manner described ismounted in a case Z of subthe heads ofthe screwsdS, the nut i2 and thecontact screw y' and with clearance holes for screws k2 by which theporcelain base, a is retained in position. A resilient mounting isprovided by tting the screws k2 with` spring` washers k3 which aredisposed either below the nuts 7b4 or between the base a and thepartition Z1 or in both positions. The screws k2 also pass throughconducting plates Z2 which extend along the lower face of the partitionZ1 and serve to receive terminal screws Z3. y n

yIn order to permit of the setting of the contact screw i so that 'thedetector may become operative when a slow rise in temperature exceeds adetermined limit, the screw is provided with a pointer 7'1 to operateover a graduated disc 7'2 adapted to t around the screw i over thepartition ll and -be secured in any desired position of adjustment as,for example, may be determined during manufacture for the purpose ofcompensating variations of setting or otherwise. By the setting of thepointer to a particular temperature indicated upon the dial and thuseffecting the rotation of the contact screw j, the normal air gapbetween the contact screws y and h is varied accordingly.

The inner contacts and the inner element c are advantageously protectedagainst dust by a channel section screen m tting loosely over theelement c and provided with an opening through which the contact screw gmay extend. The casing is advantageously closed by means of a gridlikecover Z4 permitting free access of the atmos phere to the elements b, c.c

In the operation of the detector a sudden rise of temperature causes theelement b to expand more rapidly than the element c in View of thelagging of the latter, and a circuit is therefore closed between thecontact screws g and h. During a long and gradual rise in temperature,such as is due to seasonal change, the elements b, c

expand together and approximately nochange takes place in the air gapbetween the contact screws g `and h so that the device remains stillsensitive to a sudden rise of temperature which is eiective.- to causefurther expansion of the element b. Should, however, the temperatureexceed the limit as determined by the setting of the contact screw :ithe device becomes operative by the engagement of the screws h and y'.In an installation involving the use of four of the detectors as shownin Figure 6, the detectors n are connected in parallel to the secondaryof a mains transformer o and their circuits are completed through relaycoils p respectively controlling indicating-lampsA pL-the circuit beingcornpleted through a relay coil p2 which is effective to ope-rate anaudible signal such as a bell q and a relay q1 serving to close the maincircuit for the motor of a siren q2. The relay circuits are alsosupplied from the secondarysideof the mains transformer o which iseffective also to supply current to a relay r adapted in the event offailure ofthe mains supply to close a local circuit .through a batteryr1 and signal or alarm bell r2. l It will be understood that theinvention is not limited to the details oi construction hereinbeforedescribed, nor to the application o the device foruse as a liredetector. It may be applied merely for the purpose of controllingtemperature conditions, for example, in refrigerators, stores and other"situations where the maintenance of determined temperature conditionsare desirable or essential. n n l I claim: l. A thermal switch,particularly for usein automatic temperature change alarm devices,wherein provision is made Afor establislfling` an electric alarm circuitupon either a sudden'ternperature change of a predetermined amountor aslow continued temperature change, comprising ari linsulating fbase',projecting seats at the ends of said base, two .thermal yelements of thesame `mass :and material, Vsupported at their ends on said .projectingseats-and bridging said base, insulation lagging on one lofsaid thermalelements, electrical contacts `.carried :by .and moving with said.thermal elements, and a .contact of fixed location, whereby kupcrn arapid temperature rise differential distortion of the two thermalelements operates to establish .an alarm .circuit through one pair of:contacts and yupon a slow temperature rise substantially uniformdistortion of the .two thermal elements operates to establish'an alarmcircuit through a second pair of contacts.

.2. A thermal switch, particularly for use 1n 'automatic temperaturechange alarm devices, wherein Vprovision :is made for establishing anelectric alarm circuit 'upon either a sudden temperature change of :apredetermined amount or a lslow continued temperature change, comprisingan insulating base, yprojecting seats at the endof said base, twodifferential thermal elements supported at their ends on said projectingseats and bridging said base, contacts carried by and moving with saidthermal elements, and a contact of fixed location, vall of said contactsbeing in alinement, whereby upon a rapid temperature rise differentialdistortion of the two thermal elements operates :to establish an alarmcircuit through one pair of contacts and upon a slow temperature risesubstantially uniform distortion of the two thermal elements operates toestablish an alarm circuit through a second pair of contacts.

3. A thermal switch, particularly for use in automatic temperaturechange alarm devices, wherein provision is made for establishing anelectric alarm circuit upon either a sudden ternperature change of apredetermined amount or a slow continued temperature change, comprisingan insulating base, projecting seats at the ends of said base, twothermal elements of the same mass and material, supported at their endson said projecting seats and bridging said base, insulation lagging onone of said thermal elements, electrical contacts carried by and movingwith said thermal elements, and a contact of fixed location, wherebyupon a rapid temperature rise differential distortion of the two thermalelements operates to establish an alarm 'circuit through one pair ofcontacts and upon a slow temperature rise substantially uniformdistortion of the two thermal elements operates to establish an alarmcircuit through a. second pair of contacts, all of said contacts beingin alinement.

4. A thermal switch, particularly for use in automatic temperaturechange alarm devices, wherein provision is made for establishing anelectric alarm circuit upon either a sudden temperature change of apredetermined amount or a slow continued temperature change, comprisingan insulating base, projecting seats at the end of said base, twodifferential thermal elements supported at their ends on said projectingseats and bridging said base, contacts carried by and moving with saidthermal elements, a contact of fixed location and means for adjustingthe gap between cooperating contacts, whereby upon a rapid temperaturerise differential distortion of the two thermal elements operates toestablish an alarm circuit through one pair of contacts and upon a slowtemperature rise substantially uniform distortion of the two thermalelements operates to establish an alarm circuit through a second pairyof contacts.

5. A thermal switch, particularly for use in automatic temperature`change alarm devices, wherein provision yis made for establishing anelectric alarm circuit upon either a. sudden temperature change of apredetermined amount or a slow continued temperature change, comprisingan insulating base, a rigid .frame lcontaining said base, a resilientmounting between said frame and said base, projecting seats at the endof said base, two differential 'thermal elements supported at `the endson said projecting seats and bridging said base, contacts .carried byand moving with said thermal elements, and a contact of fixed location,whereby upon va rapid temperature rise differential distortion of thetwo thermal elements operates t0 establish an alarm circuit through onepair of contacts and upon a slow temperature rise substantially uniformdistortion of the two thermal elements operates to establish an alarmcircuit through a second pair of contacts.

6. A thermal switch, particularly for use in automatic temperaturechange alarm devices, wherein provision is made for establishing anelectric alarm circuit -upon either a sudden temperature change of apredetermined amount or a slow continued .temperature change, compris--ing an insulating base, projecting seats .at the end of said base, twodifferential thermal elements supported one above the other at theirends on said projecting seats and bridging said base, contacts carriedby and moving with said thermal elements, a contact of fixed location,and spacing elements separating said thermal elements and made ofmaterial having substantially the same coefficient of expansion as saidmoving contacts.

7. A thermal switch, particularly for use in automatic temperaturechange alarm devices, wherein provision is made for establishing anelectric alarm circuit upon either a sudden temperature change of apredetermined amount or a slow continued temperature change, comprisingan insulating base, inwardly inclined projecting seats at the ends ofsaid base, two differential thermal elements supported at the ends onsaid projecting seats and bridging said base, contacts carried by andmoving with said thermal elements and a contact of fixed location.

8. A thermal switch, particularly for use in automatic temperaturechange alarm devices, wherein provision is made for establishing anelectric alarm circuit upon either a sudden temperature change of apredetermined amount or a slow continued temperature change, comprisingan insulating base, inwardly inclined projecting seats at the ends ofsaid base, two differential thermal elements supported one above theother at their ends on said projecting seats and bridging said base,contacts located between, carried by and moving with said thermalelements and a contact of fixed location.

9. A thermal switch, particularly for use in automatic temperaturechange alarm devices, wherein provision is made for establishing anelectric alarm circuit upon either a sudden temperature change of apredetermined amount or a slow continued temperature change, comprisingan insulating base, inwardly inclined projecting seats at the ends ofsaid base, two differential thermal elements supported one above theother at their ends on said projecting seats and bridglill) ing saidbase, contacts located between, carried by and moving with said thermalelements, a contact of fixed location, and projecting sleeves enclosingsaid contacts.

10. A thermal switch, particularly for use in automatic temperaturechange alarm devices, wherein provision is made for establishing anelectric alarm circuit upon either a sudden temperature change of apredetermined amount or a slow continued temperature change, comprisingan insulating base, projecting seats at the ends o1 said base, twodifferential thermal elements supported at their ends on said projectingseats and bridging said base, and secured to said base by means formingpart of the circuit to be closed through contacts carried by them,contacts carried by and moving with said thermal elements and a contactof fixed location.

11. A thermal switch particularly for use in automatic temperaturechange alarm devices wherein provision is made for establishing anelectricalarm circuit upon either a sudden temperature change of apredetermined amount or a slow continued temperature change, comprisinga frame, an insulating base carried by said frame, projecting seats atVthe ends of said base, two thermal elements of the same mass andmaterial, supported at their ends on said projecting seats arranged oneabove the other and bridging said base, insulation lagging on one ofsaid thermal elements, electrical contacts carried by and moving withsaid thermal elements, a contact of fixed location, and sleevesenclosing all said contacts, whereby differential distortion of the twothermal elements operates to establish an alarm circuit through one pairof contacts and upon a slow temperature rise substantially uniformdistortion of the two thermal elements operates to establish an alarmcircuit through a second pair of contacts. c

12. A thermal switch, particularly for use in automatic temperaturechange alarm devices, wherein provision is made for establishing anelectric alarm circuit upon either a sudden temperature change of apredetermined amount or a slow continued temperature change, comprisingan insulating base, two differential thermal elements arranged one abovethe other bridging said base, contacts located between and carried bysaid thermal elements, a third contact extending from one of saidthermal elements, and a xed contact with which said third contactcooperates, whereby upon a rapid temperature rise diierential distortionof the two thermal elements operates to establish an alarmcircuitthrough one pair of contacts and upon a slow temperature risesubstantially uniform distortion of the two thermal elements operates toestablish an alarm circuit through a second pair of contacts.

CECIL HERBERT STAVE.

